1. Field of the Invention
This invention relates to a pump for pumping a liquid containing solid contaminants.
2. Description of the Prior Art
It often occurs that pumps are required to pump a liquid containing solid contaminants. The solid contaminants can cause undersirable pump wear, for example in the pump journals.
Some parts of a pump must of necessity operate in the contaminated liquid. For example, if the pump is a gear pump with side plates, then the gears will usually be made of a hard wear-resistant material. The side plates may be made of a softer material and they will therefore wear. However the wear of the side plates is usually in a uniform manner so that they remain flat and still seal perfectly for the life of the pump. The journal bearings must not be allowed to wear to any considerable extent and so they must be supplied with a lubricant. It is advantageous for the lubricant to be pumped liquid from which the solid contaminants have been removed. The cleaned liquid can also effect cooling of the journals.
Sometimes liquids are pumped that have only slight lubricative properties, for example some presently used fuels for aircraft engines. This means that more cleaned liquids must be desirably supplied to areas requiring lubrication than when liquids are being pumped that have better lubricative properties. Furthermore, because of the low lubricative properties, the cleaned liquids must desirably be cleaned to a greater extent that liquids having further lubricative properties. For example, it may be necessary to clean the liquids having low lubricative properties so well that they are free from solid contaminants larger than 2 to 3 microns particle size.